The burning of hydrocarbon fuels in the internal combustion is an exothermic reaction that releases energy in the form of pressure, temperature, and, heat. It has been generally known for some time in the automotive industry that various components within the vehicle transmit large amounts of heat which must be shielded from other heat sensitive components in the vehicle. Today's high specific power output engines operate at high exhaust gas temperatures for prolonged periods of time. These exhaust gas temperatures can sometimes be as high as 1050° C. This high exhaust gas temperature causes exhaust manifolds, turbine housings, and catalyst cans to become very hot and remain hot during engine operation.
Heat transfer from hot exhaust components during engine operation can degrade other under-hood components including, but not limited to, motor mount rubber, fluid tube sealing o-rings, plastic covers, and electrical insulation. The degradation of these components from heat exposure causes material property degradation which subjects the components to accelerated fatigue damage. Underhood heat transfer occurs by convection, conduction, and radiation. Exhaust components operating at their peak temperature tend to be dominated by radiation heat transfer. Radiation is a “line of sight” mechanism which can be reduced with reflective shielding. It is thus desirable to prevent the transfer of the radiation by shielding heat sensitive components.
To protect components from this heat, the hot exhaust components are often designed to include a heat shield. Modern downsized and boosted engines generate more under-hood heat than earlier natural aspirated configurations. Modern engines sometimes become very hot for a relatively brief period of time during the vehicle's operating life, such as when pulling a trailer or when ascending a steep hill during which time the vehicle engine uses a lot of fuel energy that, in turn, produces high exhaust gas temperature, heat shields have been designed to be larger to account for such operating conditions. To enhance heat protection, heat shields are typically made in three layers including high strength stainless steel which makes them relatively inflexible.
Mechanical fasteners are conventionally used to attach the heat shield to points on the engine. Typically the fasteners are bolts that fasten the heat shield to the hot component. Another common convention is to use studs strategically positioned on the engine and nuts that retain the shield. However, it is known that thermal cycling of the heat shield fasteners with plain threads can cause loosening over time. As a result, prevailing torque fasteners are commonly used to insure retention for the life of the vehicle.
In the event where the turbocharger or a surrounding component needs to be accessed in service, the heat shield may have to be entirely removed. Complete removal of the shield might also be required to service oil supply lines, oil drain lines, vacuum control tubes, vacuum control solenoids, exhaust systems, or manifolds.
However, removal of the heat shield may involve complications that present challenges to the repair technician. For example, there have been many instances in service where the prevailing torque fastener has broken and been difficult to remove when the heat shield has to be removed. In this case, a new turbocharger must be installed when only the prevailing torque fastener is broken. This can add significant cost to the repair procedure.
I For these reasons, it would be advantageous to provide an effective heat shield that can be sufficiently moved to allow access to an underlying component without the need to remove the prevailing torque fastener.